Vehicle sales in China declined 2.31 per cent last month to 1.80 million units, the China Association of Automobile Manufacturers (CAAM) said.
Passenger car sales alone decreased a sharper 3.36 per cent to 1.51 million, according to the group.
Stock market volatility, downside pressures on the economy, and car plate restrictions in some cities were all factors in the declines, the CAAM said.
Both rising and falling share prices hit demand for cars, CAAM secretary general Dong Yang told a news conference.
China's benchmark Shanghai Composite Index soared by more than 150 per cent in the year to its peak on June 12, and has since plunged by almost a third before bouncing more than 10 per cent in the two days to Friday's close after government support measures were introduced.
Overall auto production fell 0.22 per cent to 1.85 million vehicles in June, according to CAAM, while that for passenger cars declined 0.72 per cent to 1.59 million.
June marked the second straight month that both production and sales fell in tandem.
From January-June, vehicle sales rose 1.43 per cent on-year to 11.85 million units, it said, with passenger cars increasing 4.80 percent to 10.10 million.
China's overall auto sales reached 23.49 million vehicles last year, jumping 6.9 per cent from 2013.
Dong said he expected the increase to slow to "around three per cent" this year.
The month and half-year results announced by CAAM came after a separate industry group said on Wednesday that passenger vehicle sales fell in June, with slowing economic growth and plunging share prices denting consumer demand.
